Machines for machining or tooling are generally divided into two types.
The machines of the first type, called transfer machines, comprise a conveyor on which the work pieces to be machined are placed and which conveys these work pieces in front of each machining unit. This type of machine, which is adapted for mass production requires considerable investment and must comprise as many machining units as there are operations to be carried out; a machine of this kind is generally only suitable for a single type of workpiece.
In the machines of the second type, which are called machining center or convertible machines, the work pieces are fixed and the different machining operations are effected successively from a machining unit or from several machining units working simultaneously, on which different machining boxes may be fitted successively.
It has already been proposed to operate the convertible machines sequentially with a transfer circuit for the machining boxes, so as to reduce the loading times for the boxes. In the machines of this kind at present constructed, a machining sequence ends by completion and discharge of a work piece.